In many technical areas it is necessary to divide a larger workpiece into a plurality of generally identical shaped sections or to separate a plurality of uniform structures from a workpiece. One example is singulation of components or chips in the semiconductor industry or related industries such as, e.g., MEMS, solar or optics. In that case, a multiplicity of components are produced on a common substrate. Once the components have been completely processed, they have to be separated from one another so that they can be further individually processed.
Various requirements are made of the singulation process, e.g., high throughput, high quality and sufficiently accurate geometrical course of the resulting component edges, clean separation of layer stacks of different materials, no losses in quality of the components and low costs per singulation step. The method and the device can also be used in the same way in other technical fields, e.g., in the glass and ceramic industry.
The problem when separating a flat workpiece into a plurality of sections is explained below on the basis of application in the semiconductor industry, where various methods and devices exist for the singulation process. The components produced on substrates are usually separated with the aid of mechanical or laser-based technologies.
In addition, there are technologies combined from mechanical and laser-based methods and also plasma etching methods and separating methods by thinning by grinding.
The last two methods mentioned and the combined methods are only of secondary importance.
Independently of the separating technology chosen, in general before the separating process, the substrate to be separated is fixed on a carrier so that the substrate does not slip during processing, the components can be separated in a controlled manner and components that have already been separated are not lost. The type of fixing is chosen depending on the substrate to be processed. In microelectronics, e.g., fixing of the substrate with the aid of a single-sided adhesive film and a carrier frame is often chosen.
In the material-removing laser methods, substrate material is removed along the scribing frame with the aid of one or a plurality of pulsed laser beams until all the components have been separated.
Laser methods free of removal or free of kerfs are based on the initialization and guidance of a crack through the substrate. Examples of such separating methods free of removal are so-called stealth dicing (SD) and thermal laser beam separation (TLS).
In stealth dicing such as is used to separate workpieces, e.g., in EP 1 716 960 B1, a pulsed laser beam having a high pulse intensity generates a material weakening by nonlinear absorption in the workpiece, the workpiece subsequently being broken by mechanical action at the material weakening. However, separating substrates having a thickness of 200 μm or thicker requires a plurality of passes with the laser beam along the separating line. This increases the process time and thus reduces the throughput.
Furthermore, in this technique the workpiece must not absorb the laser radiation to an excessively great extent to be able to generate the nonlinear effects at a sufficient depth in the workpiece. It is therefore not possible to separate highly doped substrates because absorption of the laser radiation takes place too near to the surface.
Thermal laser beam separation involves separating the workpiece by generating a high thermal stress using a laser beam which is sufficiently absorbed by the workpiece. Separation by the thermal stress requires initiation of the fracture by a suitable material weakening on or in the workpiece. For this purpose, it is known to introduce a notch into the surface of the workpiece at the edge of the workpiece to be separated or along a separating line, by which notch the crack is then initiated during the subsequent high degree of local heating by the laser beam.
EP 1 924 392 B1 discloses a method, wherein, before the TLS step, by local material modification using a pulsed laser on the surface of the workpiece, a track of modified material is generated along the separating line, which results in a reduction of the breaking stress of the workpiece along the separating line. The track replaces the previously introduced notch and can also be formed with different depth along the separating line to compensate for a possibly varying thickness of the workpiece. However, a notch or a material modification introduced instead of the notch at the surface can reduce the quality of the edge of the separated section or component.
It could therefore be helpful to provide a method and a device to separate a flat workpiece into a plurality of sections which enable separation at high speed and a higher quality of the resulting edges of the sections compared with the previous thermal laser beam separation.